1. Field of the Invention
The present invention relates in general to gas valves for gas burners and in particular to an improved gas valve for a pilotless gas burner.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
There are many burner systems that use a pilot light adjacent the main burner to ignite the main burner. Such systems have shown to be unsafe because there may be a burner flame-out and an accumulation of gas which may cause an explosion.
Thus, pilotless burner systems have been developed. Such systems are shown in U.S. Pat. Nos. 3,344,835; 3,582,249; and 4,207,054. In these patents, there are no gas flow paths through the valve that will allow different amounts of gas to be fed to the burner for ignition, running at low temperatures, and running at high temperatures. Further, they have only emergency manual controls.
Typical designs of convection heaters provide gas flow into an automatic control valve that divides the gas flow into two independent circuits, the pilot burner and the main burner.
Following ignition of the pilot burner, a thermocouple responds to the presence of the flame and provides power to the automatic control valve. The power flowing into the automatic control valve allows the valve to remain open and gas to flow into the main burner. Downstream from the automatic control valve in the main burner gas circuit is a manual control valve used to control the amount of fuel to the main burner. The operator adjusts the manual control valve to provide the desired amount of heat.
There are a number of concerns with this type of arrangement. First, proper operator involvement with the multiple valve system is very important. Failure to follow operating instructions could result in accidental starting of the main burner, delayed ignition of the main burner, and operation beyond the specified range.
Accidental ignition of the main burner occurs if the pilot burner flame proves the thermocouple and the manual control valve is not in the OFF position. Delayed ignition of the main burner can occur due to improper operation of the manual control valve. Failure to open the manual control valve to the full open position during ignition may cause delayed ignition. The operator can partially close the manual control valve, which reduces main burner gas flow below a specified input rate. Operation at reduced input rate can create high carbon monoxide, odor, and/or soot from incomplete combustion.
Further, flame supervision for the pilot burner causes additional concerns such as nuisance pilot burner outage and unsupervised operation of the main burner. Heaters may be subjected to nuisance outage due to drafts extinguishing the pilot burner. Pilot burner outage deprives the thermocouple of heat necessary to produce electrical power. The loss of electrical power causes the automatic control valve to interrupt the gas flow to all burners. In addition, the unsupervised main burner may operate below minimum input rate until the heater is manually shut down. In some cases, the main burner flame could become extinguished but still the system could flow gas because the thermocouple is supervising the pilot burner.
It would be advantageous to have a single automatic control valve system wherein the automatic safety control and the manual adjustment of the main control valve are contained within one control thus reducing the number of components.